Storm drains and storm sewers help prevent floods in our neighborhood by channeling water out of streets and into nearby waterways. But what if we were able to keep rain where it falls and allow it to soak into the soil? Green infrastructure provides a potential path forward.
Gray Versus Green Infrastructure
When rain pours down from above, where does it go?
Historically, urban and suburban areas have mostly depended on gray infrastructure, like storm sewer systems, to manage stormwater. However, these systems have limited capacity. When storm sewer systems can’t keep up with a big influx of stormwater, water can flood into streets and gush into waterways.
Yet, even when gray infrastructure is working properly, stormwater runoff is still a problem. In developed areas, stormwater flows over paved surfaces and lawns instead of absorbing into the soil. As stormwater runoff travels across the landscape, it picks up pollutants and brings them along for the ride. Common runoff “hitchhikers” include lawn fertilizer, pet waste, trash, loose sediment, excess road salt, and chemical leaks from vehicles.
Most gray infrastructure storm sewer systems are designed to direct this runoff to storm drains, channel it through a network of pipes, and dump the stormwater into the nearest waterway. The water entering storm drains is not treated like wastewater in a sanitary sewer. Instead, all the pollutants picked up by stormwater runoff enter and contaminate waterways. So, while these stormwater systems can help control flooding for moderate rainfall, they don’t protect the water quality of rivers, streams, and lakes.
To protect waterways and relieve strain on storm sewer systems, communities can turn to green infrastructure, which mimics or restores natural systems. In essence, this means letting rain soak in where it falls instead of sending it elsewhere.
Green infrastructure helps rain infiltrate down into the soil, instead of flowing across the landscape as runoff. Many kinds of green infrastructure depend on plants, especially deep-rooted native plants, that aid water infiltration.
Examples of Green Infrastructure
Green infrastructure can work on a variety of scales. The following green infrastructure examples can be adopted at the neighborhood scale:
A rain garden is a shallow depression planted with native plants that are accustomed to wet conditions. The shallow depression is often amended with more permeable soils (with high sand and organic content) to aid infiltration. Usually, a downspout is directed into the rain garden. Rain gardens collect this water and allow it to seep naturally into the ground. The native plants also provide habitat for wildlife and enhance the beauty of your yard.
Bioswales are similar to rain gardens, except they tend to be made in narrow spaces, especially along roads. All bioswales are planted with vegetation that helps stormwater infiltrate into the soil, but they can vary in their complexity and level of engineering. Many homeowners opt to transform a traditional drainage ditch into a bioswale by planting it with native plants. More complex bioswales have specially engineered soil and perforated pipes that direct water downward.
Permeable pavement is designed so that rain can go through it rather than rush over it. Either there are gaps between the pavers or the pavement itself is porous. Water collects in gravel beneath the pavement and gradually seeps into the ground.
Estimates indicate that a quarter-inch of rain falling on an average home yields over 200 gallons of water. Homeowners can collect what falls on their roof into a rain barrel or cistern. The water can then be used to water gardens or wash cars. Collecting and storing rainwater reduces stormwater runoff coming from your property.
Naturalized Detention Basins
Existing stormwater features like detention and retention basins can be upgraded with a native plant buffer. Deep-rooted native plants prevent shoreline erosion, filter out pollutants, and provide habitat for birds and butterflies. Native plant buffers have additional benefits of beautifying the neighborhood with colorful flowers and blocking geese from getting to the water.
On a larger scale, communities and businesses can try green infrastructure like green roofs (roofs that incorporate plants), green streets (a coordinated effort to “green” sections of roads), and even bigger initiatives like preserving open space and restoring floodplains.
All these systems and projects aim to allow stormwater to soak into the ground, which reduces stormwater runoff, flooding, and water contamination as a result.
Diversifying Our Stormwater Infrastructure
To be clear, we don’t have to (and don’t want to) choose between gray or green infrastructure. Our communities need both to sustainably manage stormwater. However, rather than depending on costly upgrades to water treatment plants and sewer systems, we can weave green infrastructure like bioswales and permeable pavement into our cities, towns, and neighborhoods. With a multi-pronged approach to stormwater management, our communities can improve local waterway health and be more resilient to flooding.